This invention relates to instruments for measuring vertical distances and for assuring that various components of a building structure are at the same level or at specified, predetermined differences in level.
In the construction industry it is often necessary to place a plurality of structures at the same level or at different levels at known and predetermined differences between the various levels. For example, in laying tile, positioning windows vertically, positioning wall panels vertically, and the like, it is necessary that all of the particular components be at exactly the same level or at precisely predetermined level differences.
There are various methods and apparatus used in ascertaining such levels. The conventional spirit level or bubble level may be used, but when large distances between the components are involved, this approach is difficult. In addition, when one starts at a given point on a long wall, particularly a wall with corners, it is possible to accumulate errors as one progresses along the wall and end up with a non-level panel, paint line, tile line, or the like.
Most often, these craftsmen measure from the floor or some other structure which is presumed, or at least hoped, to be level. While this is satisfactory some instances, it is not reliable in many structures.
The well-know surveyor's transit is unsuited to use by tile layers, plumbers, carpenters and others who work in confined spaces and often alone. These instruments require, for efficient use, two workmen and are expensive and cumbersome. In addition, one cannot assure that a tile line, for example, which extends into several room will be level because these rooms may not be visible from a given site.
Examples of prior art leveling devices are disclosed in the following patent documents:
Japanese Patent Application 54-10409, Hitratsuka, which discloses the use of a reflected light beam to measure the surface of a liquid in two tanks in which the liquid level is always the same.
Offenlegungsschrif 27 39 975, Wittmann, which discloses a device involving two hermetically sealed chambers with interconnected pressure sensors and a device for measuring differential pressure between the chambers.
French Patent 2,515,337, Legris, which discloses a complex solid state electronic system involving two mercury filled, sealed reservoirs sealed by stretched membranes with a semiconductor film on it.
French Patent 2,542,866, Legris, which discloses an exceedingly complex electromechanical system utilizing a reservoir closed by a membrane which closes a first space containing air which limits movements of the membrane. The first space is connected to a second space which is divided by a membrane which operates switches.
U.S. Pat. No. 2,557,021, Williams, discloses systems which require a closed loop between the bottom and top of the reservoir and the gauge, an artificially applied positive pressure, or a thermal insulator jacket.
U.S. Pat. No. 2,587,998, Heath, discloses a leveling device which has a reference reservoir which is open to the atmosphere, and hence subject to spillage or leakage at the reference point, and measuring tube which is also open to the atmosphere, which requires filling for use and emptying for transport or storage.
U.S. Pat. No. 2,804,692, Karstens, which discloses an electro-mechanical system involving a plurality of mercury filled chambers with floats on the mercury and plural electrical connections between the chambers.
U.S. Pat. No. 3,310,880, Watts, discloses a system using two manometers and a liquid system comprising a body of mercury and a body of less dense colored liquid.
U.S. Pat. No. 3,645,135, Hadley, discloses an electro-mechanical system utilizing a pair of cisterns with interconnected pools of mercury and a float on the mercury in each cistern which serves as a capacitor.
U.S. Pat. No. 3,815,423, Gearhart, discloses a ruggidized altimeter one or more diaphragms as the pressure sensing device, the diaphragms separating liquids and pressurized gasses, and error compensating structures of several types.
U.S. Pat. No. 3,835,548, Gearhart, discloses a leveling apparatus including a sight tube and a connecting liquid conduit to prevent spillage of liquid or entrapment of gases.
U.S. Pat. No. 4,106,342, Sormunen, discloses a barometric type device which uses two variable volume vessels, a pressure indicator for one vessel with temperature error compensation by means of a closed vessel acting upon the variable volume vessels.
U.S. Pat. No. 4,379,367, Legris, discloses a device relies upon a very dense liquid, e.g. mercury, and the stretching of diaphragms, membranes against the resisting force of the diaphragm material, whereas applicant relies upon a substantially non-resistant flexible bag which permits horizontal flow.
U.S. Pat. No. 4,384,410, Melugin et al, discloses a system including indicator heads connected by a liquid hose for equalizing static pressure in mercury pools and a gas hose for equalizing pressure within the heads above the mercury pools.
U.S. Pat. No. 4,563,822, Legris, discloses a masonry level which utilizes a chamber divided by a stretched diaphragm separating liquid in the lower part of the chamber and gas in the upper part of the chamber. The pressure of the liquid is reflected by the stretching of the diaphragm which compresses air which, in turn actuates a switch or indicator.
U.S. Pat. No. 4,581,931, Robotti et al, discloses a system for measuring differences in levels using plural reservoirs with floats in each, the float and an electrode forming a sensor for the level of liquid in the reservoir.
U.S. Pat. No. 4,651,433, Mohr, which discloses a system which uses pressure cells connected by flexible tubing and a strain gauge for sensing differential pressure, with various compensating devices such as a bellows to reduce hysteresis errors. In the Mohr device, accuracy depends upon exact identity of diaphragm structures and/or upon exact repetition of movement of such structures over the life of the instrument. Errors in flexing result in erroneous readings.
U.S. Pat. No. 4,759,134, Chrisley, discloses a devices which uses two flexible bags, but these are both filled with air, or gas, and neither serves as a reference reservoir. The bags of Chrisley are intended, apparently, only to permit the transmission of atmospheric pressure to the liquid column without permitting evaporation or contamination of the liquid.
Laser transits are even less suited to applications as described because of its great expense and the great amount of time required to set up the equipment.
There is a great and long-standing need for an inexpensive but accurate measuring and leveling device which will assure that components are exactly level with each other, vertically, or are at exactly predetermined differences in vertical position, as may be desired in particular instances. It is to a solution of this long-standing problem and meeting this serious need in the building and construction industries that the present invention is directed.